1. Technical Field
The present invention relates to a parallel link mechanism and an industrial robot.
2. Related Art
General requirements for industrial robots include increased operation speed, improved operation accuracy, and, in certain operation sites, enhanced cleanliness. Particularly, there are demands that the industrial robots be used under particular circumstance involving use of specific gases or chemicals. One known vertical movement shaft mechanism of a SCARA robot includes a ball screw provided in a vertical movement shaft. The mechanism has a bellows as a protecting member for preventing generation of dust and leakage of grease from the interior of an arm. Through contraction of the bellows, the vertical movement shaft mechanism ensures improved cleanliness while maintaining operation speed and operation accuracy at relatively high levels.
However, when the bellows contracts, the pressure in the vertical movement shaft mechanism changes, inducing the dust generation and the grease leakage. It is thus difficult to maintain the increased cleanliness of the vertical movement shaft mechanism having the bellows. Further, to sufficiently prolong mechanical life of the bellows of the vertical movement shaft mechanism, the bellows must be formed of material selected from a limited range. This makes it difficult to operate the vertical movement shaft mechanism having the bellows under the aforementioned particular circumstances.
To solve the problem, a vertical movement shaft mechanism of an industrial robot including a parallel link mechanism, but not a bellows, has been proposed. Specifically, as described in JP-A-2002-326181, first arm is connected to a fixed base and a connection base while second arm is connected to the connection base and a movable base. A drive motor is provided in the fixed base. A spur gear is arranged in the interior of the connection base. The drive motor rotates the spur gear through a reducer. The spur gear thus transmits rotational force to the two arms, selectively raising and lowering the movable base.
However, in this mechanism, the drive motor, or a drive source, is fixed to the fixed base. Therefore, when assembling the industrial robot, the rotational axis of the drive motor must coincide with the rotational axis of the arms. This complicates assembly of the industrial robot.
To maintain relatively high cleanliness of the industrial robot, cables are arranged in the fixed base or the arms. For enabling such internal wiring, the industrial robot employs a hollow motor as a drive motor. This enlarges the sizes of devices provided in the industrial robot.